232 



How a Complex Animal Uses Food unit iv 



Fig. 231 The man wearing a vest is using the Shaefer prone pressure method of arti- 

 ficial respiration. At what times is it useful to know how to give artificial respiration? 



(AMERICAN RED CROSS) 



center. (It is in the part of the brain 

 called the niediilla oblojigata.) 



The nerve messages leave the breathing 

 center at a fairly regular rate. Many fac- 

 tors affect the rate at which the nerve 

 messages leave the center. One of these 

 factors is the amount of carbon dioxide 

 in the blood. This factor affects the 

 breathing rate in the following way. 

 When there is an unusual amount of oxi- 

 dation there is also an unusually large 

 amount of carbon dioxide in the blood. 

 Thus the breathing center is stimulated 

 to send out impulses faster. As a result 

 you breathe faster and deeper and your 

 lungs exhale more air rich in carbon di- 

 oxide. Because of this, more and more 

 carbon dioxide diffuses out of the lung 

 capillaries; gradually the concentration 

 of carbon dioxide in the blood is again 

 decreased to normal and you once more 

 breathe more slowly. Determine your 

 normal breathing rate and the rate after 



moderate exercise. Follow the suggestions 

 in Exercise 7. Certain sensations, such as 

 cold due to the sudden chilling of the 

 skin, also change the breathing rate. So 

 do emotions, such as fright or anger. 



There is a certain amount of conscious 

 control of breathing. You can decide to 

 take a deep breath or to stop breathing, 

 for example. But you cannot ordinarily 

 prevent it, or, as we say, hold your 

 breath, for more than two minutes. 



"Artificial respiration." All cells need 

 a constant supply of oxygen, particularly 

 the brain cells. The damage that results 

 from completely cutting off the oxygen 

 supply from the brain cells for as little 

 as ten minutes can never be repaired. 

 But even after a person's breathing is 

 interfered with for any reason, such as 

 filling the lungs with water (this is what 

 happens in drowning), or with poisonous 

 gases, or as the result of an electric shock, 

 the blood is still delivering oxygen to 



